Clamp for fixing the seat post of a bicycle

ABSTRACT

A clamp for fixing a seat post ( 14 ) to a seat tube ( 12 ) provided with a slit ( 18 ) set in a longitudinal vertical plane (A). The clamp comprises:  
     a pair of deformable branches (24 a , 24 b ) defining a through hole having a cylindrical inner surface ( 20 );  
     a slit ( 22 ) between the aforesaid elastically deformable branches (24 a , 24 b ); and  
     a tightening screw ( 26 ) set in such a way as to bring up to one another two surfaces (30 a , 30 b ) facing one another of said slit ( 22 ) and to reduce the diameter of said cylindrical surface.  
     In a mounted configuration in which the aforesaid tightening screw ( 26 ) extends in a position corresponding to the through slit ( 18 ) of the seat tube ( 12 ), the slit ( 22 ) of the clamp ( 10 ) opens out onto the aforesaid cylindrical surface ( 20 ) in an area that is displaced with respect to the slit ( 18 ) of the seat tube ( 12 ).

[0001] The present invention relates to a clamp for fixing a seat post to a seat tube of a bicycle.

[0002] As is known, the saddle of a bicycle is carried by a tubular element (seat post) which is slidably inserted inside a vertical tube, namely, the seat tube, of the bicycle frame. The seat tube carrying the seat post is provided with a through slit made in an end portion of the tube, which bestows on said end portion characteristics of elastic deformability in the radial direction. The end portion of the seat tube is tightened against the outer surface of the seat post by means of a clamp having a slit which is set aligned to the slit of the seat tube and which is radially compressed by means of a screw which brings two elastically deformable branches of the clamp up to one another. For aesthetic reasons, the tightening screw is set on the side of the seat tube that faces the rear part of the bicycle.

[0003] Recently there have been introduced on the market seat posts made of carbon fiber, which consist of a fiber fabric embedded in a matrix of plastic material. A seat post made of carbon fiber makes it possible to obtain a reduction in weight as compared to a component having the same characteristics which is made, for instance, of an aluminium alloy or similar light alloys.

[0004] The traditional solution described previously for fixing the seat post to the seat tube presents a serious drawback in the case where the seat post is made of a carbon-fiber fabric embedded in a matrix of plastic material. The present applicant has found that, when a clamp of a traditional type is tightened around the end portion of the seat tube, the two internal edges defined by the through slit of the seat tube are deformed inwards and tend to cut into the outer surface of the seat post. These incisions form points of initiation of failure, which in certain cases may lead to failure of the seat post.

[0005] The purpose of the present invention is to overcome the aforesaid drawback by providing a simple and effective solution that does not entail the need to modify the seat tubes with respect to current solutions and that makes it possible to keep the tightening screw set in the rear part of the seat tube.

[0006] According to the present invention, the above purpose is achieved by a clamp having the characteristics specified in claim 1.

[0007] The present invention will now be described in detail with reference to the attached drawings, provided purely by way of non-limiting example, in which:

[0008]FIG. 1 is a schematic perspective view illustrating a seat-post assembly provided with a clamp according to the present invention;

[0009]FIG. 2 is a cross-sectional view according to the line II-II of FIG. 1;

[0010]FIG. 3 is an elevation according to the arrow III of FIG. 2;

[0011]FIG. 4 is a cross-sectional view similar to that of FIG. 2 and illustrating a second embodiment of the present invention; and

[0012]FIG. 5 is an elevation according to the arrow V of FIG. 4.

[0013] With reference to FIG. 1, number 10 designates, as a whole, a seat-post assembly for a bicycle, comprising a seat tube 12, a seat post 14 and a clamp 16.

[0014] With reference to FIG. 2, the seat tube 12 has, in a traditional way, a through slit 18 which extends as far as the top end of the seat tube 12. The through slit 18 is set in a longitudinal vertical plane the trace of which, in the plane of representation of FIG. 2, is indicated by the axis A. The slit 18 is situated on the side of the seat tube 12 that faces the rear part of the bicycle.

[0015] The clamp 16 is made of metal material, such as aluminium or one of its alloys, and has a cylindrical surface 20 designed to compress from outside the top end portion of the seat tube 12. The clamp 16 has a through slit 22 which defines two elastically deformable branches 24 a, 24 b. The two deformable branches 24 a, 24 b are elastically brought up to one another so as to reduce the diameter of the cylindrical surface 20 by tightening a screw 26. According to the present invention, the clamp 16 is configured in such a way that, in an assembled configuration in which the screw 26 is set in a position corresponding to the slit 18, the slit 22 opens out onto the cylindrical surface 20 in a position that is displaced with respect to the slit 18 of the seat tube 12. Tests carried out by the present applicant have shown that the misalignment between the slits 22 and 18 guarantees that, during tightening of the screw 26, the end portion of the seat tube 12 will close radially without producing a deformation inwards of the edges 28.

[0016] In the embodiment illustrated in FIG. 2, the slit 22 of the clamp 16 has two surfaces 30 a, 30 b facing one another, which are plane, parallel to one another and inclined with respect to a plane orthogonal to the longitudinal axis A of the tightening screw 36. The direction of the screw 36 is determined in such a way that the surfaces 30 a, 30 b facing one another of the slit 22 remain constantly parallel to one another during tightening of the screw 26. Thanks to the configuration of the clamp 16, the mutual approach of the two facing surfaces 30 a, 30 b takes place without producing a concentration of forces on the edges of the seat tube 12 that are adjacent to the slit 28. This makes it possible to obtain radial closing of the seat tube 12 with a mutual approach in the tangential direction of the edges facing one another of the slit 18, without any deformation inwards of the edges 18. In this way, the risk is eliminated of producing incisions on the outer surface of the seat post 14, which could lead to initiation of failure.

[0017]FIG. 4 illustrates a variant of the clamp according to the present invention. The items corresponding to the ones previously described are designated by the same reference numbers. Unlike in the embodiment previously described, the screw 26 extends according to an axis transverse to the longitudinal axis A. Also in this variant embodiment, the slit 22 of the clamp is displaced in the tangential direction with respect to the slit 18 of the seat tube 12. Also in this case, the mutual approach between the two surfaces 30 a 30 b facing one another of the slit 22 is along a direction tangential to the tube and in a position that does not entail a concentration of forces on the edges 28 of the seat tube 12. The main difference with respect to the embodiment described previously is that in the present case the surfaces 30 a, 30 b facing one another of the slit 22 are step-like surfaces with respective end portions which are parallel to one another. The end portions that open out onto the inner cylindrical surface are substantially orthogonal to the axis of the screw 26, i.e., they are substantially parallel to a plane orthogonal to the axis of the screw, but could also be inclined with respect to said plane.

[0018] Of course, without prejudice to the principle of the invention, the details of construction and the embodiments may vary widely with respect to what is described and illustrated herein, without thereby departing from the scope of the present invention as defined in the ensuing claims. 

1. A clamp for fixing a seat post (14) to a seat tube (12) provided with a slit (18) set in a longitudinal vertical plane (A), comprising: a pair of deformable branches (24 a, 24 b) defining a through hole having a cylindrical inner surface (20); a slit (22) between the aforesaid elastically deformable branches (24 a, 24 b); and a tightening screw (26) set in such a way as to bring up to one another two surfaces (30 a, 30 b) facing one another of said slit (22) and to reduce the diameter of said cylindrical surface, characterized in that, in a mounted configuration in which the aforesaid tightening screw (26) extends in a position corresponding to the through slit (18) of the seat tube (12), the slit (22) of the clamp (10) opens out onto the aforesaid cylindrical surface (20) in an area that is displaced with respect to the slit (18) of the seat tube (12).
 2. The clamp according to claim 1, characterized in that the aforesaid surfaces (30 a, 30 b) facing one another are plane surfaces that are substantially parallel to one another.
 3. The clamp according to claim 1, characterized in that the aforesaid surfaces (30 a, 30 b) facing one another are step-like surfaces with end portions that are substantially parallel to one another.
 4. The clamp according to claim 2, characterized in that the aforesaid plane surfaces (30 a, 30 b) facing one another are inclined with respect to a plane orthogonal to the axis of the tightening screw (26).
 5. The clamp according to claim 3, characterized in that the end portions of said step-like surfaces (30 a, 30 b) facing one another which open out onto the inner cylindrical surface (20) are substantially orthogonal to the axis of the aforesaid tightening screw (26).
 6. The clamp according to claim 3, characterized in that the end portions of said step-like surfaces (30 a, 30 b) facing one another which open out onto the inner cylindrical surface (20) are inclined with respect to a plane orthogonal to the axis of the aforesaid tightening screw (26). The foregoing substantially as described and illustrated and for the purposes herein specified. 